72 THE SKELETON OF THE CAT. 
articulates with the os magnum (/) and third metacarpal, while 
the radial surface articulates with the trapezium (d). 
The third metacarpal (3) is the longest, and its base is 
rhomboidal with a projecting dorsoradial angle separated by a 
groove from the rhomboid surface. The proximal end articu- 
lates with the os magnum (/) and second metacarpal; the 
radial surface of the proximal end with the second, and the 
ulnar surface with the fourth, metacarpal. 
The fourth metacarpal (4) has a base similar in form to that 
of the third, and when placed in position with the fifth the two 
form a hemispherical facet which articulates with the unciform 
(g) and os magnum (/). The fourth metacarpal articulates by 
its radial side with the third, and by its ulnar side with the fifth. 
The fifth metacarpal (5) articulates by its proximal end 
with the unciform (g), and by the radial side of its proximal 
end with the fourth metacarpal. 
Digits (Fig. 51).—The first digit of the hand is called the 
pollex (thumb), the second the index, the third the medius, 
the fourth the annularis, the fifth the minimus. 
The first digit has two phalanges, each of the others three 
phalanges. 
Phalanges (Fig. 51, 2, 7, 2).—The phalanges of the proxi- 
mal row (7) are elongated, flattened dorsoventrally and curved 
so as to be longitudinally convex dorsad. All have thickened 
ends. The proximal end is notched, and its proximal surface 
looks dorsad and is concave for the head of the metacarpal. 
The distal end is pulley-shaped, and the pulley surface extends 
farther on to the ventral than on to the dorsal surface, and 
serves for articulation with the middle phalanx. 
The phalanges of the middle row (/) are like those of the 
proximal row, but shorter. The proximal surface is triangular 
and marked by a median facetted ridge. The whole surface is 
smooth and adapted to the distal end of the phalanx of the first 
row. The distal end is transversely elongated, so as to be 
cylindrical, and projects more toward the ulnar than toward 
the radial side. The distal phalanx (4) articulates with this: 
cylinder so that when it is fully extended it lies on the ulnar 
side of the middle phalanx. 
